The present invention relates to a threaded clamping plug for interconnecting two implants of a spinal osteosynthesis instrumentation or other implants.
In spinal osteosynthesis instrumentations heretofore employed, in particular those of the xe2x80x9cCOTREL-DUBOUSSETxe2x80x9d type (U.S. Pat. Nos. 4,641,636 and 4,815,453), the component elements are placed in position and assembled by means of small screws. At the end of the screwing, the surgeon causes their fracture so as to remove their head, which requires cutting the rods if it is necessary to proceed to a subsequent removal of the instrumentation which is consequently rendered relatively awkward.
Further, the measurement of the clamping torques of the screws requires additional instruments the precision of which is not always satisfactory.
Objects of the invention are to provide, on one hand, an assembling element which allows an easier subsequent disassembly of the instrumentation if need be and, on the other hand, a system integrated with the plug which affords a precise predetermined clamping torque.
According to the invention, the threaded plug comprises two coaxial parts separated by a fracture initiating line, and each part is provided with a print coaxial with the other print, the first part being adapted to permit the screwing of the second threaded part on an implant up to a predetermined fracture torque between the two parts, the print provided on the second part permitting an optional subsequent unscrewing of the latter.
The threaded part may be screwed in a tapped hole provided in the corresponding implant, or on the screw thread of the body of a vertebral anchorage element (screw or hook) to ensure the connection of this element with a rod, or on a threaded rod of a transverse connection device between two longitudinal osteosynthesis rods.
It must be understood that these three embodiments of the plug according to the invention are not intended to be limitative, since the invention has a very wide scope in osteosynthesis instrumentations.
Thus, after fracture, when the prescribed torque is exceeded and the two parts are separated, the second part can be if necessary unscrewed by means of its print which is adapted to a suitable tool so that the device can be disassembled.
The magnitude of the fracture torque is a function of the depth of the fracture initiating line and can be easily adjusted to the desired magnitude. It is therefore possible to obtain for the clamping torque an improved precision relative to clamping torques employed up to the present time with the usual screws, since it is possible to determine the fracture torque in a much more precise manner than with the usual means which involve the use of a relatively imprecise torquemeter.